This invention relates to a pinion stopper arrangement for a starter motor which enables to shorten the axial length of the rotary output shaft and to have a stopper with a simple structure.
FIG. 1 is a sectional view of a conventional pinion stopper arrangement for a starter motor disclosed in Japanese Utility Model Laid-Open No. 55-53727, and FIG. 2 is a sectional view taken along line II-II of FIG. 1. In FIGS. 1 to 4, an output shaft 2 of an armature 1 to be driven by a magnetic field unit has a large-diameter step portion 2A, and helical splines 3 are formed in the outer periphery of the step portion 2A.
To the helical splines 3, a spline tube 5 of a pinion mechanism composed of a pinion 4, the spline tube 5, an over-running clutch 6 is thread-engaged so as to be movable in the axial direction.
As best seen in FIG. 4, the output shaft 2 of the armature 1 has formed thereon the large-diameter step portion 2A in which the helical splines 3 are formed and a small-diameter escape portion 2B in which an inner helical splines 5A of the spline tube 5 can be rotated.
The length L.sub.1 of the escape portion 2B is longer than the length L.sub.2 of the inner helical spline 5A and has a smaller inner diameter than the helical spline 3.
Also, as apparent from FIG. 2, the helical spline 3 is formed by providing the step portion 2A with a plurality of first grooves 2C helically extending over the entire axial length of the large-diamter portion 2A and a plurality of second grooves 2D extending parallel to the first grooves 2C but has shorter length.
In the intermediate portion of the step portion 2A, an annular groove 17 is formed, in which a clip 19 as shown in FIG. 3 having inwardly bent portions 18 at a pitch substantially equal to that of the inner helical splines 5A of the spline tube 5 is engaged as shown in FIG. 1.
As is well known, the starter motor comprises a shift lever 10, a solenoid switch 12, a plunger 13, a torsion spring 14, a gear case 15, a ring gear 16 and a center plate 20.
In the structure as above described, the pinion mechanism is first assembled. After the clip 19 is fitted in the annular groove 17 of the step portion 2A of the output shaft 2, the ridge portions of the inner helical spline 5A of the spline tube 5 of the pinion mechanism are correspondingly positioned with respect to the inwardly bent portions 18 and inserted from the side of the ring gear 16 until the inner helical spline 5A is positioned within the reduced-diameter escape portion 2B of the output shaft 2. Then, when the splines are disengaged from each other, two splined members are rotated relative to each other by an angle corresponding to one ridge.
This causes the ridge portion of the helical splines 5A to abut against one end of the clip 19, whereby the pinion mechanism cannot be dislodged from the output shaft 2.
Since the pinion stopper mechanism of the conventional starter motor is constructed as above described, the output shaft 2 must have the escape portion 2B for allowing the inner helical splines 5A of the spline tube 5 to be rotated therein, making the axial dimension of the output shaft 2 enevitably large.
Also, the second shorter grooves 2D for preventing the movement of the inner helical spline 5A of the spline tube 5 must be formed in the output shaft 2 independently of the first groove 2C, making numbers of the manufacturing steps large and difficult.